Speeding up MadGraph5_aMC@NLO.

In this paper we will describe two new optimisations implemented in MadGraph5_aMC@NLO, both of which are designed to speed-up the computation of leading-order processes (for any model). First we implement a new method to evaluate the squared matrix element, dubbed helicity recycling, which results in factor of two speed-up. Second, we have modified the multi-channel handling of the phase-space integrator providing tremendous speed-up for VBF-like processes (up to thousands times faster). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1140/epjc/s10052-021-09204-7.